Because blood stage infections produce most clinical manifestations of malaria, drug development has primarily focused on the development of schizonticides targeting Plasmodium falciparum, the causative agent of the most severe form of human malaria. Increased funding and a growing awareness of the problem of parasite resistance have helped to push a number of new schizonticides into the developmental pipeline and even clinical trials. On the other hand, few of these drug candidates are effective against malaria exoerythrocytic stages, and even fewer are likely to provide a radical cure for P. vivax malaria. The need for drugs which can act as a replacement for primaquine is even more urgent as malaria eradication becomes a higher priority for the world health community. In order to stimulate drug development activity against hepatic stages, more work is needed to understand hepatic stage biology and to discover targets whose activity is essential for both hepatic and blood stage development. I will use a chemical genetic approach to investigate pathways that are critically essential to both blood and hepatic parasite development and then characterize the target(s) revealed by this approach. Specifically, I will grow parasites under sub-lethal concentrations of small molecules with activity against blood and hepatic stage parasites until the parasites acquire low level resistance to the small molecules. I will use genome-scanning to determine the likely target(s). Mutations will be engineered into sensitive parasite strains to prove that they cause resistance. Likely targets will be further characterized using immuno and electron microscopy and localization studies, as well as disruption studies. The work may lead to a better understanding of how to treat tissue stage malaria, provide new antibiotic resistance genes, and provide information about how eukaryotic pathogens become resistant to drugs. PUBLIC HEALTH RELEVANCE: Many antimalarial drugs alleviate symptoms but do not necessarily result in a complete cure because some malaria parasites are able to persist asymptomatically in the liver for months or years. The inability to eliminate cryptic liver forms creates a barrier to malaria eradication. We propose to find new targets that are critical to the liver stages as well as the blood stages with the long term aim of designing better drugs.